Fabry disease is an inherited X-linked recessive metabolic disorder resulting from the deficient activity of the lysosomal enzyme, a- galactosidase A (AGA). In affected hemizygous males, the progressive deposition of substrate in lysosomes of vascular endothelial and smooth muscle cells causes occlusive vascular disease. To date there is no specific treatment for this condition. Both enzyme replacement and gene therapy are under consideration, but carrying out these trials in human will be difficult and time-consuming. An animal model for Fabry disease will be valuable to develop such therapeutic regimes. In order to generate an animal model we disrupted AGA genomic locus in mouse embryonic stem cells by homologous recombination and generated AGA null mice. Although these mice showed a complete lack of AGA activity, they appeared clinically normal at 10 weeks of age. Ultrastructural studies analysis revealed concentric lamellar inclusions in the kidneys, and confocal microscopy using a fluorescent-labeled lectin specific for a-D-galactosyl residues showed accumulation of substrate of in the kidneys as well as in the cultured fibroblasts. Lipid analysis revealed a marked accumulation of the substrate in the liver and the kidneys. These findings indicate the similarity of the pathophysiological process in the AGA null mice and in patients with Fabry disease. Moreover, using biscistronic MDR vectors containing human AGA cDNA we have corrected AGA deficiency and accumulation of a-D-galactosyl residues in the cultured fibroblasts from the AGA null mice.